The use of reference calibration patches exposed on a roll of film to enable better exposure control during optical printing is known in the art. See for example U.S. Pat. No. 5,767,983 issued Jun. 16, 1998 to Terashita. The use of reference calibration patches has also been shown to be useful in determining correction values for scanned film data used in digital printing. See for example U.S. Pat. No. 5,667,944 issued Sep. 16, 1997 to Reem et al.; and U.S. Pat. No. 5,649,260, issued Jul. 15, 1997 to Wheeler et al. The use of reference calibration patches has been shown to be used for adjusting optical printing control for making colored copies or prints (U.S. Pat. No. 5,767,983 issued Jun. 16, 1998 to Terashita; U.S. Pat. No. 4,577,961 issued Mar. 25, 1986 to Terashita; U.S. Pat. No. 4,211,558 issued Jul. 8, 1980 to Oguchi et al.; and U.S. Pat. No. 4,884,102 issued Nov. 28, 1989 to Terashita). The use of reference calibration patches has been shown for creating transforms for calibrating exposure (U.S. Pat. No. 5,267,030 issued Nov. 30, 1993 to Giorgianni et al.).
Reference calibration patches have been shown to be recorded in a camera (U.S. Pat. No. 3,718,074 issued Feb. 27, 1973 to Davis; U.S. Pat. No. 4,365,882 issued Dec. 28, 1982 to Disbrow). Reference calibration patches have been shown to be recorded on separate apparatus devices (U.S. Pat. No. 4,260,245 issued Apr. 7, 1981 to Hujer; U.S. Pat. No. 5,452,055 issued Sep. 19, 1995 to Smart; U.S. Pat. No. 5,075,716 issued Dec. 24, 1991 to Jehan et al.). Reference calibration patches have been shown to be recorded on a photofinishing device (U.S. Pat. No. 4,881,095 issued Nov. 14, 1989 to Shidara; U.S. Pat. No. 4,464,045 issued Aug. 7, 1984 to Findeis et al.; U.S. Pat. No. 4,274,732 issued Jun. 23, 1981 to Thurm et al.; U.S. Pat. No. 5,649,260 issued Jul. 15, 1997 to Wheeler et al.; U.S. Pat. No. 5,319,408 issued Jun. 7, 1994 to Shiota).
Barcode data relating to film type and frame number is encoded on the edge of filmstrips for use in photofinishing. For example, the film format known as the Advanced Photo System (APS) as designated in the System Specifications for the Advanced Photo System, referred to as the APS Redbook available from Eastman Kodak Company, reserves specific areas on an APS format film strip to contain latent image barcode information. In particular, a lot number is available for use by a filmstrip manufacturer to encode 27 bits of digital information as described in section 8.2.4 and shown in FIGS. 100-2, 210-1, 210-4-N and 210-4-R in the APS Redbook. Optical storage and retrieval of data written in a rectangular grid aligned with the length of the medium for scanning by a linear CCD array has been disclosed in U.S. Pat. No. 4,786,792 issued to Pierce, et. al. on Nov. 22, 1988 and U.S. Pat. No. 4,634,850 issued to Pierce, et. al. on Jan. 6, 1987. Use of two-dimensional barcode symbols to store data is well known in the prior art and many such symbologies have been standardized by national and international standards organizations. For example, the Data Matrix symbology, disclosed in U.S. Pat. No. 4,939,354 issued Jul. 3, 1990 to Priddy et al., is the subject of the standards ANSI/AIM BC-11-1997 and ISO/IEC 16022:2000. A second such example, the MaxiCode symbology, disclosed in U.S. Pat. No. 4,874,936 issued Oct. 17, 1989 to Chandler et al. is the subject of the standards ANSI/AIM BC-10-1997 and ISO/IEC 16023:2000. A third such example, the Aztec Code symbology, disclosed in U.S. Pat. No. 5,591,956 issued Jan. 7, 1997 to Longacre et al., is the subject of the standard ANSI/AIM BC-13-1998. Software used to locate, decode, and detect and correct errors in symbols in a digital image file is readily available. For example, software for locating and decoding the Data Matrix and MaxiCode symbology is available as the SwiftDecoder™ software product from Omniplanar Inc., Princeton, N.J. Finally, the required scanning and digitization equipment needed to obtain digital image files from a photographic element is readily available in the photofinishing industry.
In the prior art, reference calibration patch data is matched with predetermined aim data and used to make varying levels of corrections to raise image quality. As used herein, the operation referred to as calibration includes making corrections to digital images based on measurement data obtained from reference calibration patches recorded on a photographic element and associated aim values for the photographic element. In order to carry out such a calibration, it is necessary to expose the reference patches with essentially the same exposure levels assumed in the aim. We have found that when a number of exposure devices are used to apply reference calibration patches, for example on different media manufacturing lines, it is necessary to have very exacting device to device exposure control to minimize device to device variations in reference calibration patch exposures on the photographic elements. The requirements are so demanding, that it is prohibitive to set up and keep a number of such exposure devices adequately calibrated.
Reference calibration patch exposures made at a time that differs greatly from the times at which scenes are exposed onto various locations (called frames) on the photographic element will not accurately reflect any changes in imaging characteristics of the photographic element as the element ages before exposure, referred to as raw stock keeping, or as any latent image formed by exposure ages after exposure, referred to as latent image keeping. Exposures made on a photographic element in manufacturing have shorter raw stock keeping and longer latent image keeping than images of scenes. Exposures made on a photographic element just prior to processing have longer raw stock keeping and shorter latent image keeping than images of scenes. Processing may occur at any time after exposure, so variation in latent image keeping of reference calibration patches and images of scenes naturally occurs. Exposures may occur at any time after manufacturing, so variation in raw stock keeping of reference calibration patches and images of scenes naturally occurs. We have found that a calibration based on data from reference calibration patches when used with predetermined aim data fails to compensate for keeping related differences.
We have also found that reference calibration patch exposures located on a photographic element in a location that differs from frames containing scene exposures, such as near the edge of a filmstrip or between perforations on a filmstrip (as opposed to the center of the filmstrip), result in different densities than those obtained by the same exposures in frame locations containing scene exposures. Additionally, we have found that differences in processing throughout the length of a photographic element also result in different densities. A calibration based on data from reference calibration patches when used with predetermined aim data fails to compensate for location related differences.
We have further found that data acquired from reference calibration patches on a variety of photographic elements using a variety of measurement devices vary. Devices such as densitometers, colorimeters, and image scanners use varying illumination, filtration, and sensor technologies that result in variations in density values reported for an area containing specific amounts of colorants from a given photographic element colorant set. Although a density measurement device may be calibrated to give a predetermined aim response for specific input media, we have found that even well-calibrated devices give different responses when presented with images on a variety of photographic elements. This problem is particularly troublesome if a different device is used to measure reference calibration patches than is used for measuring scene images, as a calibration based on data from such measurements, when used with predetermined aim data, fails to compensate for measurement device related differences.
We have found that pixel values obtained with an image scanner in a particular picture element or pixel, corresponding to a particular area on the photographic element, are often corrupted by inadvertent illumination, referred to as flare, impinging upon the scanner sensor. For example, assuming pixel values that increase with density, pixel values obtained for a small area with a low density surrounded by a large area with a higher density are higher than pixel values obtained from a large area with the same low density as the small area due to higher absorption of stray light by the surrounding area. Conversely, pixel values obtained for a small area with high density surrounded by a large area with lower density are lower than pixel values obtained from a large area with the same high density as the small area due to lower absorption of stray light by the surrounding area. In a typical scene image, local and overall density variations in the area of the photographic element being scanned tend to produce an effective surrounding density that is significantly above the minimum density and below the maximum density. Accordingly, the pixel values obtained in individual pixels of a scene image that correspond to areas with lower densities tend to be higher than they would be in a large area with a uniform low density and pixel values obtained in individual pixels of a scene image that correspond to areas with higher densities tend to be lower than they would be in a large area with a uniform high density. Unfortunately, the image content of a reference calibration target comprising a set of reference calibration patch exposures is often far from that of a typical scene. Significant areas of very low or very high density are found in such reference calibration targets that influence pixel values measured in reference calibration patches either as compared to pixel values that would be obtained either from a larger patch area or from a patch area surrounded by densities typical of a scene image. Accordingly, data obtained from reference calibration patches are corrupted in a different way than data obtained in a scene image, making a calibration based on reference calibration patches and a predetermined set of aim values inaccurate.
We have found that indiscriminate use of data from reference calibration patches containing corruption from dust, scratches, or other imperfections makes a calibration based on reference calibration patches and a predetermined set of aim values inaccurate.
There is a need therefore for an improved method of calibration that minimizes the problems noted above.